Field of the Invention
The invention relates in general to power management, and more particularly to a power management method and associated device for a power path powering an electronic device.
Description of the Related Art
With progress in technologies, industries demand higher standards on the power consumption of electronic devices. For example, Energy Star, a program backed by the US government, is a plan that assists businesses and consumers to be more environmentally friendly. The Energy Star plan specifies the power efficiency and standby power of many electrical appliances. By acquiring an Energy Star certification, a product is proven to conform to the Energy Star specification that ensures the efficiency of the product, thus leading to increased purchasing of the product by consumers.
Taking a computer monitor for example, the Energy Star defines the power consumption of three operation modes of the computer monitor. These three operation modes are an on mode, a sleep mode and an off mode. The on mode refers to a state in which an image on a screen changes according to image signals transmitted from a computer host; the sleep mode refers to a reduced-power state when the screen shows a blank image, and may be switched to the on mode by a request signal sent from the computer host; the off mode is a state in which, although the computer monitor is plugged in to power, the screen is basically not powered, displays no image, and awaits for a user or a computer signal to switch to the on mode. For example, the user may press a power key of the computer monitor to switch the computer monitor from the off mode to the on mode. According to the 2006 Energy Star specification, the power consumption for a computer monitor in the sleep mode must be below two watts, and the power consumption in the off mode must be below one watt.
Apart from reducing the power consumption of the computer monitor as much as possible in the off mode, various functions need to be considered in circuit design of the computer monitor. One of these functions is that, for example, the computer monitor needs to allow a user to determine whether the computer monitor is plugged in to an AC power source, including when operating in the off mode. Another function is that, for example, when the computer monitor loses and regains AC power, the computer monitor needs to automatically restore to its operational status from before AC power was lost.